1. Peniocereus greggii (Engelmann) Britton & Rose, Contr. U.S. Natl. Herb. 12: 428. 1909.
Desert night-blooming cereus, Arizona queen-of-the-night
Cereus greggii Engelmann in F. A. Wislizenus, Mem. Tour N. Mexico, 102. 1848
Shrubs, erect to sprawling, usually inconspicuous. Roots turnip-shaped, usually 15-30 × 5-12 cm (much larger ones known). Stems gray-green to gray, simple or with 2-5 branches, 40-120(-300) cm, distally 8-20 mm diam., at midlength ca. 10 mm diam., often narrowed toward base; wood hollow, solid-surfaced cylinders, 4-7 mm diam.; ribs 4-6, prominent; areoles (3.5-)12(-15) mm apart along ribs, circular to elliptic, 2-5 × 2 mm. Spines (9-)11-15(-17) per areole, usually in 3 vertical rows; abaxial 3-5 spines appressed, yellowish white throughout or only at tips, to 3 mm, puberulent when young; adaxial spines black, subulate, to 1 mm. Flowers: nocturnal (remaining open next day), 15-25 cm; scales of flower tubes green, tipped red or brown; outer tepals greenish white with brown to reddish midstripes; inner tepals white or lightly tinged cream or pink (or rarely all rose-pink), lanceolate-attenuate, apiculate, 4-7 cm, attenuate to mucronate; stamens 2.5 cm; anthers cream-yellow, 2 mm; style white, 10-14 cm; stigma lobes 9-11, white. Fruits bright red, darkening in age, ellipsoid, 60-90 × 40-50 mm. Seeds 3-4 × 2-2.5 mm. 2n = 22.
Varieties 2 (2 in the flora): sw United States, w Mexico.